A communication system is formed, at a minimum, by transmitter and a receiver interconnected by a communication channel. Communication signals transmitted by the transmitter are transmitted upon the communication channel to be received by the receiver.
A radio communication system is a communication system in which the communication channel is formed of one or more frequency bands of the electromagnetic frequency spectrum. Because a fixed or hard-wired connection is not required to be formed between the transmitter and the receiver, a radio communication system is advantageously utilized when the use of such fixed or hard-wired connections would be inconvenient or impractical.
A cellular communication system is a type of radio communication system. When the infrastructure, hereinafter referred to as the network, of the cellular communication system is installed throughout a geographical area, a subscriber to the cellular system is generally able to communicate telephonically in the system when positioned at any location in the geographical area encompassed by the system.
While conventional, terrestrial-cellular communication networks have been installed throughout significant portions of the world, some areas are without such networks. In areas of low population density, for instance, a terrestrial-cellular communication network might not be commercially viable. Also, existing, terrestrial-cellular networks have also been constructed pursuant to various different standards.
A radiotelephone, sometimes hereinafter referred to also as a "user terminal", operable in one of the communication systems is sometimes not operable in others of the cellular communication systems. Even in an area in which a cellular communication network has been installed, a user might not be able to communicate pursuant thereto if the user attempts to utilize a user terminal constructed to be operable only with another one of the cellular communication networks.
Satellite-cellular communication systems have been proposed which, when implemented, shall permit a user to communicate telephonically by way of the satellite-cellular communication system when positioned at almost any location. By transmitting down-link signals between a satellite-based transceiver and the user terminal and up-link signals between the user terminal and the satellite-based transceiver, telephonic communication shall be possible between the user terminal and the satellite-based transceiver. By effectuating additional communication links between the satellite-based transceiver and a ground station, the user of the user terminal shall be able to communicate telephonically with another party by way of the ground station and the satellite-based transceiver.
Because of the inherent efficiencies of digital communication techniques, many already-installed cellular communication networks have been converted, and many newly-proposed cellular communication systems are being designed, to utilize digital communication techniques. Other communication systems similarly utilize, or are planned to be converted to or to utilize, digital communication techniques.
To function properly, particularly when the communication system utilizes digital communication techniques, the user terminal must be synchronized with a network station of the cellular communication network. Conventionally, synchronization sequences are transmitted by the network station to the user terminal to synchronize the user terminal with the network station. Other communication systems similarly utilize conventional, synchronization sequences for similar purposes.
Synchronization of the user terminal with a transmitter which transmits the synchronizing sequences thereto typically requires a significant number of processing steps to be performed. A correlation is typically performed between signals received by the receiver and a stored synchronization word. When a sequence of symbol bits of the received signal exhibits a high correlation with the stored synchronization word, a determination is made that such received symbol bits form the synchronization sequence transmitted to the receiver. Synchronization of the receiver with the network station is thereby effectuated when the format of the signal transmitted to the receiver is known. That is to say, when the synchronization sequence is transmitted to the receiver according to a known format, locations of other signal components of signals transmitted to the receiver can be determined once the location of the synchronization sequences are determined.
Conventionally, groups of received symbol bits are each correlated with the stored synchronization word. Conventionally, to determine the correlation of the received symbol bits with the stored synchronization word requires a first-order number, N, of calculations to be performed upon each group of symbol bits. The number of processing steps required to perform correlations upon each group of symbol bits received by the receiver quickly becomes a very significant number, requiring a significant amount of processing to determine the reception of the synchronization sequences.
When the signals transmitted to the receiver are subjected to high levels of attenuation or multi-path distortion, detection of the synchronization sequences is more difficult as the synchronization sequences might be distorted or attenuated during their transmission to the receiver.
Any manner by which to provide a high margin synchronization sequence to a receiver to permit the receiver to become synchronized with a transmitter while requiring a lesser number of processing steps to be performed would be advantageous.
It is in light of this background information related to synchronization of a receiver with a transmitter, such as a user terminal of a cellular communication system, that the significant improvements of the present invention have evolved.